Genetics background of β-thalassemia (3.5 kb deletion) in Southern Thailand: Haplotype analysis using novel reverse dot blot hybridization

β-thalassemia (β-thal) (3.5 kb deletion or NC_000011.10:g.5224302-5227791del3490bp) is a common mutation in southern Thailand. This study aimed to determine genetic diversity in subjects with β-thal (3.5 kb deletion) alleles and to ascertain the origin of this mutation using haplotype and phylogenetic analysis. The study was carried out on members of the southern Thai population, including 45 normal individuals, 116 heterozygous β-thal (3.5 kb deletion) and one homozygous β-thal (3.5 kb deletion). The 5'-haplotype in β-globin gene cluster was examined using newly developed reverse dot blot hybridization (RDB) and compared with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The results showed 100% concordance between the haplotype patterns of these two methods. From a total of 324 chromosomes, nine haplotypes were segregated. Haplotype H2 (+ - - - -) was the predominant haplotype observed in all 118 β-thal (3.5 kb deletion) chromosomes, which revealed a single origin. The phylogenetic tree demonstrated that β-thal (3.5 kb deletion) has an older genetic defect in this region. Moreover, the developed RDB is simple, less time-consuming, inexpensive, and does not restriction enzyme digestion.

Association Between Genetic Polymorphisms and Hb F Levels in Heterozygous β-Thalassemia 3.5 kb Deletions

Single nucleotide polymorphisms (SNPs) in several genetic modifying factors have been related to Hb F levels, including ^Gγ XmnI polymorphism, B-cell lymphoma/leukemia 11 A (BCL11A), HBS1L-MYB intergenic polymorphism (HMIP) and a mutation in the Krüppel-like factor 1 (KLF1). This study aimed to determine whether genetic variability of these modifying factors affects Hb F levels in heterozygous β-thalassemia (β-thal) 3.5 kb deletion (NC_000011.10: g.5224302-5227791del13490bp). A total of 111 β-thal 3.5 kb deletion carriers with Hb F levels ranging from 0.9 to 18.4% was recruited for this study. Genotyping of SNPs including HBG2 rs7482144, HMIP rs4895441 and rs9399137, BCL11A rs4671393 and KLF1 rs2072596 was identified. Multiple regression analyses showed that only two SNPs (HMIP rs4895441 and rs9399137) influenced Hb F levels. Interestingly, a combination of these two SNPs was associated with higher Hb F levels. Our study is the first to demonstrate that the rs4895441, rs9399137 of HMIP are associated with elevated Hb F levels in the heterozygous β-thal 3.5 kb deletion.

Prenatal diagnosis of α- and β-thalassemias in southern Thailand

We report our work on prenatal diagnosis of α-thalassemia, β-thalassemia and other hemoglobinopathies in southern Thailand. DNA-based diagnosis was offered to 1906 pregnancies at risk for thalassemia using a combination method of multiplex-PCR and reverse dot blot analysis to detect seven α-globin and 47 β-globin mutations. The most commonly detected mutation of α⁰-thalassemia was a South-East Asian deletion (98%), followed by a Thai deletion (2%). Twenty-eight β-globin mutations were identified. Fourteen common mutations, including cod 19 A-G (18.6%), cod 41/42 -TCTT (14.4%), IVS1#5 G-C (13.2%), 3.5 kb deletion (9.2%), cod 17 A-T (7.7%), -28 A-G (7.3%), IVSI#1 G-T (7.1%), 12.5 kb deletion (δβ)⁰ (5.7%), HPFH6 (4.2%), IVS2#654 C-T (2.7%), 45 kb deletion (1.9%), Asian Indian-inversion-deletion Gγ(Aγδβ)⁰ (1.6%), cod 41 -C (1.5%) and cod 71/72 +A (1.3%) were detected, accounting for 96.5% of all mutations detected. The most common hemoglobin variant was Hb E, accounting for 97.86%. Prenatal diagnosis of 1906 couples at risk showed 22.0% normal, 51.2% carrier and 26.8% affected. The present study provides important information for diagnosis and control of severe thalassemia diseases.